The article concentrates on the study of the lexicon of customary law in different subdialects of the Yakut language. Despite the vast area of Yakut language distribution, the language is characterized by its monolithic character and lack of significant dialectal differences. Dialectologists distinguish only the subdialects with some lexical and grammatical peculiarities. In this regard, the considered category of vocabulary is not characterized by great diversity. This phenomenon is connected with the archaization and withdrawal from use of the lexicon of customary law due to the inclusion of Yakut society in the field of Russian legislation. The terms borrowed from the Russian language appeared to replace native terminology. Another reason is the development of mass writing and the transition to common literary norms of the language. The largest amount of dialectal vocabulary is noted in the terminology of kinship and property, which continues to function actively. In addition, individual examples are present in such branches of customary law as criminal law, property relations, social and administrative structure. The identified vocabulary is categorized into groups of colloquialisms and semantic categories in accordance with the branches of Yakut customary law. The article attempts to analyze the etymological analysis. A significant number of words are borrowings from the Russian language. The considered lexical units are formed as a result of semantic shift, phonetic adaptation of Russisms. In the field of criminal law, many lexemes are represented by euphemisms that emerged in order to express taboo concepts.